Random

• To avoid bias, the sample must be randomly selected so each organism has an equal chance of being counted; if a sample is not random, it is unrepresentative and may give an overestimate of biodiversity, if deliberately selected
• Advantage: Data not biased by selective sampling; disadvantage: It may not cover all areas equally and species with low presence may be missed
• Area of habitat is mapped out using long tape measures (often area is 10m^2) and using pairs of random co-ordinates (generated by a calculator), the quadrats are positioned within the square for sampling
• A quadrat is a wireframe of a fixed size e.g. 1m^2, 0.5m^2 or 0.25m^2 that defines the sample area size
• Number of samples depends on habitat size, time available, and number of species in habitat, if two habitats are being compared, the same number should be taken for each
• The larger the sample, the more representative the data; it is possible to calculate mean data to assess how many are valid, once it is stable, you have had enough (10 is often sufficient)
• Recording results: Need a suitable results table, prepared in advance, that allows room to record all species identified
• For species richness, presence of a species is recorded; qualitative data, it is unlikely all species are listed, for species evenness, the number of each species is recorded (more meaningful for biodiversity); quantitative